1. Field of the Invention
This invention relates generally to bogus or counterfeit document detection methods and, particularly to the method for printing or otherwise making a product document that will be nonreplicable by any scanning-type copying device such as a copying machine, video opticon, and the like.
2. Discussion of the Prior Art
Many methods have been employed, as well as myriad machines, in order to verify the authenticity of documents such as bank notes, checks, licenses and identification pictures. Currency, security and other valuable documents are, in most cases, printed or lithographed onto high quality media such as silk, rice paper or high content rag paper. The printing may be black and white or color and most often employs one of two printing processes--line intaglio or gravure (rotogravure). The first, intaglio, is a process widely used in the production of bank notes, securities, stamps and engraved documents. The distinctive sharpness of fine lines and readily discernable differences in ink thickness that the process produces make it a preferred technique for production of bank notes and securities. The gravure pattern is similar to that of intaglio with the exception being that rather than fine channels appearing between lines, the gravure etching consists of extremely small square--like cells laid out in a grid array. In both of these methods of printing, the ink is held within the line troughs or square wells and transferred to the print media, under high mechanical pressures, by capillary movement. The gravure printing process is generally used for catalogs, magazines, newspaper supplements, cartoons, floor and wall coverings, textiles and plastics.
Other methods such as the Dultgen half tone intaglio process and the Henderson process (often referred to as direct transfer or inverse half tone gravure) are often used in place of the gravure but do not distinguish significantly over the previously described processes relative to the grid-like orientation of lines and dots (formed when the square-type wells are used). Since the purpose of the instant invention is to provide methods and a product made from such methods for preventing replication of any important document, in black and white or color, the remaining portion of this disclosure shall concentrate more heavily on intaglio printed surfaces rather than gravure or its variations. Further, most discussion will be confined to intaglio because a general disclosure relating to line printing would necessarily include dot printing as well since, by the inventor's definition, a dot is merely a line of short length, its length being equivalent to its width. Thus, the square-type well or dot of the gravure printing process may be likened to the intaglio wherein two sets of parallel lines or lineations, one orthognal to the other, are employed.
After an intense, exhaustive search of the literature and patents on file at the United States Patent and Trademark Office, the instant inventor turned from the more current methods and machines for document verification and devised the instant invention product and the methodology for its preparation. The philisophical motivation for the instant invention is twofold: first, in order to determine whether a document is counterfeit, it is not necessary to determine its authenticity--one only has to prove that a single element of the document is bogus; and second, a labored examination in order to determine a singular bogus element would be conducted best if the document were to contain within itself the means that would prevent its replication. In order to achieve these two objectives, it was necessary for the instant inventor to blend his skill in printing with the knowledge of optics that is readily available to one of ordinary skill. Accordingly, and being long familiar with the phenomenon of moire that often occurs in printing, he reasoned that what had always occurred as a problem could be turned to the advantage of society in the elimination of the counterfeiting of face--value documents. For the edification of the reader it will suffice to say that the moire is a serious problem in color reproduction. It is the occurance of an interference pattern caused by the over printing of the screens in colorplates (similar effects can be observed by superimposing two pieces of a fine grid network such as window screening). Indeed, the technique of rotating half tone screens, when making the negatives for a printing plate, has been developed in order to avoid the moire interference. Often it appears as the geometrical design that results when a set of straight or curved lines is superposed onto another set. If a grating design, made of parallel black and white bars of equal width, is superposed on an identical grating, moire fringes will appear as the crossing angle is varied from about one second of arc to about 45 degrees. The pattern will consist of equispaced parallel fringes; but, if two gratings of slightly different spacing are superposed, fringes will appear (known as "beat" fringes) which shift positions much faster than does the displacment of one grating with respect to the other. Finally, it has been noted that a different kind of moire pattern results when two families of curves of different colors are superposed--fringes of a third color are produced. An application of the use of the moire phenomenon is disclosed in U.S. Pat. No. 3,109,239, issued to the instant inventor and titled SCREEN ANGLE INDICATOR. This disclosure reveals a method that is used to locate, view and visually align the angle of half tone screens without the aid of magnification. The screen half tone which is to be read is placed over a screened 360 degree or 90 degree protractor which contains five half tone screens of about 60% in value 21/2 degrees to the right and 21/2 degrees to the left at angles of 45 degrees, 60 degrees, 75 degrees, 90 degrees and 105 degrees. When the screen is turned within 5 degrees of a predetermined angle, a moire interference pattern begins to visually form and, as the screen comes closer, a much darker and larger moire pattern becomes visible. When the screen reaches the exact angle to be located, the moire pattern appears greatly enlarged and, in fact, turns either black or white. Any misalignment appears as an enlarged moire or secondary pattern; thus the screen angle indicator creates magnified images by interference in order to identify and locate or position a half tone screen at a given angle. It became apparent to the instant inventor, therefore, that the moire pattern, rather than as an indicator which is gradually removed from an image, may also be used as an indicator of some perhaps latent defect in a document. More appropriately, there had to be some way in which a pattern could be included in an image by printing it in a selected pattern. Then, when the image was viewed through a superposed grid, such as previously discussed, a moire pattern would be observed according to the degree in which the patterns interfered with each other. Moreover, if one were to reduce the moire apparatus to its simplest form, that is, such as viewing some background through the common parallel-stake snow fence (suggested by the previous description of parallel black grid lines spaced by parallel white or clear areas of equal width), and if the pattern over which it is superposed is formed of lines and dots that are equally spaced from each other (whether parallel or curvilinear), but a fraction off the pitch (or spacing) of the overlain grid, the observer would be deprived of a high percentage of the background field of vision. Thus, the background image, if formed of the line and dot printed grid, would be rendered nonreplicable to any apparatus being used to record the view. It is this particular aspect of moire pattern creation that is used by the instant inventor to create this invention. Further, he also recognized that because the modern copy machine, whether it be a standard color tone copier or a laser printer, scanned the image to be copied with a fixed-pitch scanning system, it was unnecessary to devise overlay grid means. In fact, the modern replicator contains such a grid in the fixed--pitch, parallel scan format that is used to view the image to be replicated.
When apprised by friends, who dealt in the field of secure documents and negotiable instruments, that the advent of the color copier had almost overnight imbued the amateur counterfeiter with the ability to reproduce such documents as currency notes, travelers checks, and the like, it became readily apparent to the instant inventor that conventional means of document authentication would be insufficient to stop an almost exponential increase in the preparation of bogus documents. For example, with but minor skill and manipulation of controls, a modern color copier, especially of the laser type, can make a most credible reproduction of United States Bank Notes, travelers checks, drivers' licenses and identification cards. So good are the replicas, that department store clerks, grocery clerks, bank tellers, change machines, and a host of others have been duped by the introduction of these replicated documents into the market place. Major efforts of others attempting to solve this problem at costs totaling several million dollars have all been unsuccessful. In particular, no one heretofore has found a way to provide an original banknote or important document which embodies the two often-sought features of a copy-proof instrument; for example, one which to the unaided eye is both indistinguishable from a prior (genuine) item and which is capable only of obviously bogus copier replication.